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'-X T OXNET PIP - DDT Page 4 of 5
<br /> synergism may be possible between DDTOs metabolites and organophosphate (cholinesterase-inhibiting)
<br /> pesticides to produce greater toxicity to the nervous system and higher mortality (82). Aroclor
<br /> (polychlorinated biphenyls, or PCBs) may result in additive effects on eggshell thinning (82).
<br /> . Effects on Aquatic Species: DDT is very highly toxic to many aquatic invertebrate species. Reported 96-hour
<br /> LC50s in various aquatic invertebrates (e.g., stoneflies, midges, crayfish, sow bugs) range from 0.18 ug/L to
<br /> 7.0 ug/L, and 48-hour LC50s are 4.7 ug/L for daphnids and 15 ug/L for sea shrimp (55). Other reported 96-
<br /> hour LC50s for various aquatic invertebrate species are from 1.8 ug/L to 54 ug/L (82). Early developmental
<br /> stages are more susceptible than adults to DDTOs effects (82). The reversibility of some effects, as well as the
<br /> development of some resistance, may be possible in some aquatic invertebrates (55). DDT is very highly toxic
<br /> to fish species as well. Reported 96-hour LC50s are less than 10 ug/L in coho salmon (4.0 ug/L), rainbow
<br /> trout(8.7 ug/L), northern pike (2.7 ug/L), black bullhead (4.8 ug/L), biuegill sunfish (8.6 ug/L), largemouth
<br /> bass (1.5 ug/L), and walleye (2.9 ug/L) (55). The reported 96-hour LC50s in fathead minnow and channel
<br /> catfish are 21.5 ug/L and 12.2 ug/L respectively (55). Other reported 96-hour LC50s in largemouth bass and
<br /> guppy were 1.5 ug/L and 56 ug/L respectively (82). Observed toxicity in coho and chinook salmon was
<br /> greater-in smaller fish than in larger (82). It is reported that DDT levels of 1 ng/L in Lake Michigan were
<br /> sufficient to affect the hatching of coho salmon eggs (3). DDT may be moderately toxic to some amphibian
<br /> species and larval stages are probably more susceptible than adults (81, 82). In addition to acute toxic effects,
<br /> DDT may bioaccumulate significantly in fish and other aquatic species, leading to long-term exposure. This
<br /> occurs mainly through uptake from sediment and water into aquatic flora and fauna, and also fish (82). Fish
<br /> uptake of DDT from the water will be size-dependent with smaller fish taking up relatively more than larger
<br /> fish (82). A half-time for elimination of DDT from rainbow trout was estimated to be 160 days (82). The
<br /> reported bioconcentration factor for DDT is 1,000 to 1,000,000 in various aquatic species (83), and
<br /> bioaccumulation may occur in some species at very low environmental concentrations 55 . Bioaccumulation
<br /> Y P rY ( )
<br /> may also result in exposure to species which prey on fish or other aquatic organisms (e.g., birds of prey).
<br /> . Effects on Other Animals (Nontarget species): Earthworms are not susceptible to acute effects of DDT and
<br /> its metabolites at levels higher than those likely to be found in the environment, but they may serve as an
<br /> exposure source to species that feed on them (82). DDT is non-toxic to bees; the reported topical LD50 for
<br /> DDT in honeybees is 27 ug/bee (82). Laboratory studies indicate that bats may be affected by DDT released
<br /> from stored body fat during long migratory periods (82).
<br /> ENVIRONMENTAL FATE
<br /> . Breakdown in Sail and Groundwater: DDT is very highly persistent in the environment, with a reported
<br /> half life of between 2-15 years (83, 84) and is immobile in most soils. Routes of loss and degradation include
<br /> runoff, volatilization, photolysis and biodegradation (aerobic and anaerobic) (73). These processes generally
<br /> occur only very slowly. Breakdown products in the soil environment are DDE and DDD, which are also
<br /> highly persistent and have similar chemical andphysical properties (82, 84). Due to its extremely low
<br /> solubility in water, DDT will be retained to a greater degree by soils and soil fractions with higher proportions
<br /> of soil organic matter (82). It may accumulate in the top soil layer in situations where heavy applications are
<br /> (or were) made annually; e.g., for apples (72). Generally DDT is tightly sorbed by soil organic matter, but it
<br /> (along with its metabolites) has been detected in many locations in soil and groundwater where it may be
<br /> available to organisms (82, 83). This is probably due to its high persistence; although it is immobile or only
<br /> very slightly mobile, over very long periods of time it may be able to eventually leach into groundwater,
<br /> especially in soils with little soil organic matter. Residues at the surface of the soil are much more likely to be
<br /> broken down or otherwise dissipated than those below several inches (3). Studies in Arizona have shown that
<br /> volatilization losses may be significant and rapid in soils with very low organic matter content (desert soils)
<br /> and high irradiance of sunlight, with volatilization losses reported as high as 50% in 5 months (85). In other
<br /> soils (Hood River and Medford) this rate may be as low as 17-18% over 5 years (85). Volatilization loss will
<br /> vary with the amount of DDT applied, proportion of soil organic matter, proximity to soil-air interface and the
<br /> amount of sunlight (82).
<br /> . Breakdown of Chemical in'Surface Water: DDT may reach surface waters primarily by runoff, atmospheric
<br /> transport, drift, or by direct application (e.g. to control mosquito-borne malaria) (73). The reported half-life for
<br /> DDT in the water environment is 56 days in lake water and approximately 28 days in river water (83). The
<br /> main pathways for loss are volatilization, photodegradation, adsorption to water-bornc particulates and
<br /> sedimentation (73) Aquatic organisms, as noted above, also readily take up and store DDT and its metabolites.
<br /> Field and laboratory studies in the United Kingdom demonstrated that very little breakdown of DDT occurred
<br /> in estuary sediments over the course of 46 days (82). DDT has been widely detected in ambient surface water
<br /> sampling in the United States at a median level of 1 ng/L (part per trillion) (73, 76).
<br /> . Breakdown of Chemical in Vegetation: DDT does not appear to be taken up or stored by plants to a great
<br /> extent. It was not translocated into alfalfa or soybean plants, and only trace amounts of DDT or its metabolites
<br /> were observed in carrots, radishes and turnips all grown in DDT-treated soils (82). Some accumulation was
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